This application is based on Patent Application No. 10-43383 filed Feb. 25, 1998 in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a process for fabricating a vertical-cavity surface-emitting semiconductor laser, which is useful as an optical source for optical interconnection that optically connects chips or boards to each other or for conducting two-dimensional parallel signal processing, and to a vertical-cavity surface-emitting semiconductor laser.
2. Description of the Related Art
Vertical-cavity surface-emitting semiconductor lasers, which are easy to construct a two-dimensional array and enables high efficient coupling with fibers without use of lenses for coupling because of their illumination pattern being circular, are considered important as an optical source for optical interconnection or two-dimensional parallel signal processing and also important for the purpose of reducing power consumption because they permit extreme lowering of threshold current by means of an ultrafine-cavity structure.
FIG. 1 is a cross-sectional view showing a conventional vertical-cavity surface-emitting semiconductor laser along the direction vertical to a crystal face thereof (cf. (1) B.-S. Yoo, H. Y. Chu, H.-H. Park, H. G. Lee and J. Lee, IEEE Journal of Quantum Electronics, vol. 33, No. 10, 1997, pp. 1794-1800; and (2) C. Chang-Hasnain, Y. A., Wu, G. S. Li, G. Hasnain, K. D. Choquette, C. Caneau and L. T. Florez, Applied Physics Letters, vol. 63, No. 10, 1993, pp. 1307-1309). The laser of FIG. 1 comprises devices including a p-GaAs substrate 101, which has thereon in order a p-AlyGa1xe2x88x92yAs/AlzGa1xe2x88x92zAs (0 less than y less than z) distributed Bragg reflector (DBR) mirror 102 (the dashed portion showing AlzGa1xe2x88x92zAs and the white portion showing AlyGa1xe2x88x92yAs), a non-doped AlwGa1xe2x88x92wAs lower spacer layer 103, a GaAs/AlxGa1xe2x88x92xAs (xxe2x89xa6w) multiple quantum well active layer 104, a non-doped AlwGa1xe2x88x92wAs upper spacer layer 105, an n-AlyGa1xe2x88x92yAs/AlzGa1xe2x88x92zAs (0 less than y less than z) DBR mirror 106, a semiconductor buried layer 107, a lower electrode 108, an insulator 109, an upper electrode 110, and an element separating structure 111. The respective layers of DBR are set to a thickness corresponding to one fourth of the quotient obtained by dividing the lasing wavelength by the refractive index of each layer.
Among the devices shown in FIG. 1, an AlGaAs/AlGaAs n-i-p-i structure or an amorphous GaAs layer has been reported as the buried layer 107, each exhibiting single transverse mode lasing operation. However, the above-described structures do not achieve optical constriction due to refractive index optical waveguide but are of an anti-guide waveguide structure. Therefore, in principle, a plurality of transverse modes can occur but not a single transverse mode. In this case, higher order transverse modes are cut off to achieve a single transverse mode operation by utilizing the outer portion of the waveguide having a higher loss. However, in dynamic characteristics in which the carrier density inside the active layer varies widely, there arises the problem that an unstable operation occurs, that is, higher order modes may emerge depending on the carrier density distribution in the active layer.
A first object of the present invention is to provide a vertical-cavity surface-emitting semiconductor laser which provides single transverse mode operation that is dynamically stable as compared with a conventional vertical-cavity surface-emitting semiconductor laser.
A second object of the present invention is to provide a vertical-cavity surface-emitting semiconductor laser having a smaller element volume than a conventional vertical-cavity surface-emitting semiconductor laser which provides high speed modulation characteristics and provides single transverse mode operation that is dynamically stable as compared with a conventional vertical-cavity surface-emitting semiconductor laser.
A third object of the present invention is to provide a process for fabricating a vertical-cavity surface-emitting semiconductor laser of which transverse mode is single and dynamically more stable than a conventional vertical-cavity surface-emitting semiconductor laser.
A fourth object of the present invention is to provide a process for fabricating a vertical-cavity surface-emitting semiconductor laser having a smaller element volume than a conventional vertical-cavity surface-emitting semiconductor laser which provides high speed modulation characteristics and provides single transverse mode operation that is dynamically stable as compared with a conventional vertical-cavity surface-emitting semiconductor laser.
The above and the other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.